Nanodiamond Influence on the Nucleation and Growth of YBCO Superconducting Film Deposited by Metal-Organic Decomposition.

It was recently shown that the introduction of nanodiamond (ND) into a superconducting metal-organic deposited YBa2Cu3O7-δ (YBCO) film produces an increase in critical current density in self-field conditions (B = 0 T). Such improvement appears to be due to the formation of denser and smoother films than the samples deposited without ND. This paper presents the work done to understand the role of ND during YBCO nucleation and growth. A detailed study on YBCO+ND films quenched at different temperatures of the crystallization process was carried out. Results showed that the reaction responsible for YBCO production appeared effectively affected by ND. In particular, ND stabilizes one of the YBCO precursors, BaF2(1-x)Ox, whose conversion into YBCO requires a prolonged time. Therefore, the YBCO nucleation is slowed down by ND and begins when the experimental conditions favor both thermodynamically and kinetically the formation of YBCO along the c-axis. This effect has important implications because the growth of a highly epitaxial c-axis YBCO film enables excellent superconducting performance.

Boron-Mediated Grain Boundary Engineering Enables Simultaneous Improvement of Thermoelectric and Mechanical Properties in N-Type Bi2 Te3.

Powder metallurgy introduces small structures of high-density grain boundaries into Bi2 Te3 -based alloys, which promises to enhance their mechanical and thermoelectric performance. However, due to the strong donor-like effect induced by the increased surface, Te vacancies form in the powder-metallurgy process. Hence, the as-sintered n-type Bi2 Te3 -based alloys show a lower figure of merit (ZT) value than their p-type counterparts and the commercial zone-melted (ZM) ingots. Here, boron is added to one-step-sintered n-type Bi2 Te3 -based alloys to inhibit grain growth and to suppress the donor-like effect, simultaneously improving the mechanical and thermoelectric (TE) performance. Due to the alleviated donor-like effect and the carrier mobility maintained in our n-type Bi2 Te2.7 Se0.3 alloys upon the addition of boron, the maximum and average ZT values within 298-473 K can be enhanced to 1.03 and 0.91, respectively, which are even slightly higher than that of n-type ZM ingots. Moreover, the addition of boron greatly improves the mechanical strength such as Vickers hardness and compressive strength due to the synergetic effects of Hall-Petch grain-boundary strengthening and boron dispersion strengthening. This facile and cost-effective grain boundary engineering by adding boron facilitates the practical application of Bi2 Te3 -based alloys and can also be popularized in other thermoelectric materials.

Ru Catalyst Encapsulated into the Pores of MIL-101 MOF: Direct Visualization by TEM.

Ru catalyst nanoparticles were encapsulated into the pores of a Cr-based metal-organic framework (MOF)-MIL-101. The obtained material, as well as the non-loaded MIL-101, were investigated down to the atomic scale by annular dark-field scanning transmission electron microscopy using low dose conditions and fast image acquisition. The results directly show that the used wet chemistry loading approach is well-fitted for the accurate embedding of the individual catalyst nanoparticles into the cages of the MIL-101. The MIL-101 host material remains crystalline after the loading procedure, and the encapsulated Ru nanoparticles have a metallic nature. Annular dark field scanning transmission electron microscopy, combined with EDX mapping, is a perfect tool to directly characterize both the embedded nanoparticles and the loaded nanoscale MOFs. The resulting nanostructure of the material is promising because the Ru nanoparticles hosted in the MIL-101 pores are prevented from agglomeration-the stability and lifetime of the catalyst could be improved.

Protecting redesigned supercharged ferritin containers against protease by integration into acid-cleavable polyelectrolyte microgels.

HYPOTHESIS: The application of ferritin containers as a promising drug delivery vehicle is limited by their low bioavailability in blood circulation due to unfavorable environments, such as degradation by protease. The integration of ferritin containers into the polymeric network of microgels through electrostatic interactions is expected to be able to protect ferritin against degradation by protease. Furthermore, a stimuli-responsive microgel system can be designed by employing an acid-degradable crosslinker during the microgel synthesis. This should enable ferritin release in an acidic environment, which will be useful for future drug delivery applications. EXPERIMENTS: Nanoparticle/fluorophores-loaded ferritin was integrated into microgels during precipitation polymerization. The integration was monitored by transmission electron microscopy (TEM)2 and fluorescence microscopy, respectively. After studying ferritin release in acidic solutions, we investigated the stability of ferritin inside microgels against degradation by chymotrypsin. FINDINGS: About 80% of the applied ferritin containers were integrated into microgels and around 85% and 50% of them could be released in buffer pH 2.5 and 4.0, respectively. Total degradation of the microgels was not achieved due to the self-crosslinking of N-isopropylacrylamide (NIPAM). Finally, we prove that microgels could protect ferritin against degradation by chymotrypsin at 37 °C.

On the role of the metal oxide/reactive electrode interface during the forming procedure of valence change ReRAM devices.

One of the key issues of resistive switching memory devices is the so called "forming" process, a one time process at a high voltage, which initializes the resistive switching at significantly lower voltages. With this study we identify the influence of the different layers - namely the insulating oxide layer (ZrO2 and Ta2O5) and the reactive ohmic electrode layer (Hf, Ta and Pt) - on the forming voltage and the pristine capacitance of the devices. For this, the forming voltage and pristine capacitance is measured in dependence of the oxide layer thickness with different electrodes. The different slopes of the forming voltage - thickness relation for different top electrodes give an indication that the reactive ohmic electrode is oxidized from the oxide layer underneath and that the degree of the oxidation depends on the thickness of the oxide layer as well as the materials used for the oxide and electrode layer. This finding could be confirmed by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) measurements. From the electrical measurements and the TEM images the thickness of the oxidized electrode layer could be estimated. The degree of the oxidation depends on the oxygen affinity of the oxide and electrode material. The interface dependent (thickness independent) part of the forming voltage is determined by the material of the electrode. The magnitude of this interface voltage could be correlated to the oxide free energy of the electrode material. These results can support the ongoing research towards resistive switching memory devices with a very low forming voltage or forming free behaviour.

Metallic filamentary conduction in valence change-based resistive switching devices: the case of TaOx thin film with x∼ 1.

The resistive switching in metal-oxide thin films typically occurs via modulation of the oxygen content in nano-sized conductive filaments. For Ta2O5-based resistive switching devices, the two current models consider filaments composed of oxygen vacancies and those containing metallic Ta clusters. The present work tries to resolve this dispute. The filaments in Ta2O5 were formerly shown to exhibit the same electrical transport mechanisms as TaOx thin films with x∼ 1.0. In this paper, sputtered thin films of pure ß-Ta and of TaOx with different oxygen concentrations are studied and compared in terms of their structure and electrical transport. The structural analysis reveals the presence of Ta clusters in the TaOx films. Identical electrical transport characteristics were observed in the TaOx films with x∼ 1.0 and in the ß-Ta film. Both show the same transport mechanism, a carrier concentration on the order of 1022 cm-3 and a positive magnetoresistance associated with weak antilocalization at T < 30 K. It is concluded that the electrical transport in the TaOx films with x∼ 1.0 is dominated by percolation through Ta clusters. This means that the transport in the filaments is also determined by percolation through Ta clusters, strongly supporting the metallic Ta filament model.

Controlled Crystal Growth of Indium Selenide, In2Se3, and the Crystal Structures of α-In2Se3.

In2Se3 has been known for over 100 years and recently attracted interest as a promising candidate for a variety of applications, such as solar cells, photodiodes, and phase-change memories. Despite the broad concern for possible uses, its polymorphism and structure are poorly characterized. By combining X-ray diffraction, transmission electron microscopy, and quantum-chemical calculations, we present here the crystal structures of two layered room-temperature polytypes: 3R and 2H In2Se3. Both polymorphs are stacking variants of the same Se-In-Se-In-Se layers comprising two coordination environments for the In atoms, one tetrahedral and one octahedral. By using chemical-bonding analysis, we look at the different In positions in α-In2Se3 and compare them to those in the metastable ß-phase.

Interfaces between Model Co-W-C Alloys with Various Carbon Contents and Tungsten Carbide.

Interfaces between alloys simulating binders in WC-Co cemented carbides and tungsten carbide were examined on the micro-, nano-, and atomic-scale. The precipitation of fine WC grains and η-phase occurs at the interface of the alloy with the low carbon content. The precipitation of such grains almost does not occur in the alloy with the medium-low carbon content and does not take place in the alloy with the high carbon content. The formation of Co nanoparticles in the binder alloy with the medium-low carbon content was established. Interfaces in the alloy with the medium-low carbon content characterized by complete wetting with respect to WC and with the high carbon content characterized by incomplete wetting were examined at an atomic scale. The absence of any additional phases or carbon segregations at both of the interfaces was established. Thus, the phenomenon of incomplete wetting of WC by liquid binders with high carbon contents is presumably related to special features of the Co-based binder alloys oversaturated with carbon at sintering temperatures.

Bending Gold Nanorods with Light.

V-shaped gold nanoantennas are the functional components of plasmonic metasurfaces, which are capable of manipulating light in unprecedented ways. Designing a metasurface requires the custom arrangement of individual antennas with controlled shape and orientation. Here, we show how highly crystalline gold nanorods in solution can be bent, one-by-one, into a V-shaped geometry and printed to the surface of a solid support through a combination of plasmonic heating and optical force. Significantly, we demonstrate that both the bending angle and the orientation of each rod-antenna can be adjusted independent from each other by tuning the laser intensity and polarization. This approach is applicable for the patterning of V-shaped plasmonic antennas on almost any substrate, which holds great potential for the fabrication of ultrathin optical components and devices.

Large pinning forces and matching effects in YBa2Cu3O(7-δ) thin films with Ba2Y(Nb/Ta)O6 nano-precipitates.

The addition of mixed double perovskite Ba2Y(Nb/Ta)O6 (BYNTO) to YBa2Cu3O(7-δ) (YBCO) thin films leads to a large improvement of the in-field current carrying capability. For low deposition rates, BYNTO grows as well-oriented, densely distributed nanocolumns. We achieved a pinning force density of 25 GN/m(3) at 77 K at a matching field of 2.3 T, which is among the highest values reported for YBCO. The anisotropy of the critical current density shows a complex behavior whereby additional maxima are developed at field dependent angles. This is caused by a matching effect of the magnetic fields c-axis component. The exponent N of the current-voltage characteristics (inversely proportional to the creep rate S) allows the depinning mechanism to be determined. It changes from a double-kink excitation below the matching field to pinning-potential-determined creep above it.